Forming negative ions
Negative ions are called An atom or group of atoms that have gained electrons and become negatively charged. Most anions are formed from non-metals..
Oxygen is in group 6. An oxygen atom has six electrons in its outer shell. The atom is more stable if it has a full outer shell.
An oxygen atom can gain two electrons to fill its outer shell. It will still have eight positive protons but will now have ten negative electrons. This gives it an overall charge of -2.
This charge is added to the symbol for oxygen, O2-. It is always written as 2- and not -2. The name of oxygen changes when naming it as an ion. The ion is called an oxide ion.
The name of a Element that is a poor conductor of electricity and heat, and which forms acidic oxides. ion is different to the name of its element:
| Atom name | Ion name |
| Oxygen | Oxide |
| Fluorine | Fluoride |
| Bromine | Bromide |
| Iodine | Iodide |
| Sulfur | Sulfide |
| Atom name | Oxygen |
|---|---|
| Ion name | Oxide |
| Atom name | Fluorine |
|---|---|
| Ion name | Fluoride |
| Atom name | Bromine |
|---|---|
| Ion name | Bromide |
| Atom name | Iodine |
|---|---|
| Ion name | Iodide |
| Atom name | Sulfur |
|---|---|
| Ion name | Sulfide |
Question
Fluorine is in group 7. It has atomic number 9 and mass number 19.
- How many outer electrons does a fluorine atom have?
- What is the charge of a fluoride ion and what is its symbol?
- How many protons does a fluoride ion have?
- How many neutrons does a fluoride ion have?
- fluorine has 7 electrons in its outer shell (it is in group 7 and its electron arrangement is 2.7)
- a fluoride ion has a charge of -1. Its symbol is F-
- number of protons = atomic number, so there are 9 protons
- number of neutrons = mass number - atomic number, so 19 - 9 = 10 neutrons
Explaining reactivity in group 7
Group 7 non-metals attract an extra electron to complete their outer shell. The outer electron shell gets further from the nucleus moving down the group. This means that the extra electron is less strongly attracted, so the reactivity of group 7 gets less going down the group.